(1) Field of the Invention
The present invention relates to a machine continuously advancing in an operating direction for maintaining or rehabilitating a railroad track consisting of two rails fastened to successive ties resting on ballast. The machine comprises a machine frame supported on two undercarriages for continuous movement in the operating direction, the undercarriages being spaced apart in this direction and the machine frame having a front end and a rear end with respect to this direction, a carrier frame arranged between the undercarriages, a track lifting and lining unit vertically adjustably mounted on the carrier frame, a ballast tamping unit vertically adjustably mounted on the carrier frame, the ballast tamping unit comprising pairs of reciprocatory and vibratory tamping tools immersible in the ballast upon vertical adjustment of the ballast tamping unit for tamping ballast under respective ones of said ties, and a drive linking the carrier frame to the first machine frame for longitudinally displacing the carrier frame with respect thereto.
(2) Description of the Prior Art
To obtain a degree of track position accuracy and an extended duration of the accurately positioned track required for the ever increasing train speeds encountered in railroads, Canadian patent No. 1,191,739 proposes the use of a group of successively arranged track working machines for bringing a railroad track into a desired position and to fix it in that position. Such a succession of coordinated track maintenance or rehabilitation machines, of which the most important one always is a track leveling, lining and tamping machine, has become known as a "mechanized track work train" (MDZ) whose individual machines are coordinated with respect to their work but which advance and operate independently of each other. Each individual machine has its own operator's cab and its own drive, which requires an operating crew for each machine. The mechanized track work train disclosed in the Canadian patent comprises a continuously advancing ballast cleaning machine followed, in the operating direction, by an intermittently advancing track leveling, lining and tamping machine and, finally, a continuously operating track stabilization machine. In this manner, the cleaned ballast discharged from the ballast cleaning machine into the track bed is tamped under the ties as the track is leveled and/or lined to obtain a desired track position, and the track is then lowered into a permanent position by compacting the ballast under controlled conditions by the vibratory rail-engaging tools of the track stabilization machine. This type of mechanized track work train, whose individual machines may be changed according to the desired results, has been used very successfully in track maintenance and rehabilitation work but it requires relatively expensive individual machines and large work crews, considering the requirement for individual control personnel for each machine.
In an article entitled "The modern systems for track maintenance and track renewal" in "Eisenbautechnik", No. 4, 1986, pages 20/21, it has been disclosed that the efficiency of a mechanized track work train (H-MDZ) may be increased by the use of a continuous action track leveling, lining and tamping machine with a longitudinally displaceable carrier frame for the ballast tamping and track lining and leveling units, which may or may not be supported by an undercarriage on the track rails, such as disclosed, for example, in U.S. Pat. No. 4,627,358, dated Dec. 9, 1986. This continuously advancing machine is followed, in the operating direction, by a continuously operating ballast planing and compacting machine with which the ballast is leveled and/or moved into zones where the rail-engaging vibratory tools of the following dynamic track stabilization machine operate. This high-efficiency mechanized track work train also has been used with great success but also requires relatively expensive machinery and a large work crew.
A continuously advancing track leveling, lining and tamping machine for tamping ballast under the successive ties of a railroad track is also known from U.S. Pat. No. 4,643,101, dated Feb. 17, 1987. The machine comprises a machine frame having a front end supported on an undercarriage, and a hydraulic cylinder drive longitudinally displaceably links a carrier frame to the machine frame. A track lifting and lining unit is vertically adjustably mounted on the carrier frame, and a ballast tamping unit is vertically adjustably mounted on the carrier frame, the ballast tamping unit comprising pairs of reciprocatory and vibratory tamping tools immersible in the ballast upon vertical adjustment of the ballast tamping unit for tamping ballast under respective ones of said ties. The carrier frame cyclically moves from tie to tie while the machine frame advances non-stop. An operator's cab is mounted at a rear end of the machine frame within sight of the ballast tamping unit and the machine frame has a projecting rear end portion extending to the center of a succeeding auxiliary frame on which the projecting rear end machine frame portion is supported. The auxiliary frame is supported on the track rails by front and rear undercarriages so that the longitudinally displaceable carrier frame is arranged between two undercarriages, i.e. the front undercarriages of the machine frame and the auxiliary frame. Two track stabilization units with vertically adjustable vibratory track stabilizing devices are mounted on the auxiliary frame between the front and rear undercarriages thereof. The structure and support of the machine frame is such that a portion of the heavy weight of the ballast tamping means is transferred to the auxiliary frame, which enhances the effectiveness of the track stabilization units in lowering the track to its desired stabilized end position. This is a specialized machine integrating ballast tamping and stabilization. It frequently requires the subsequent use of a ballast plow for planing and shaping the ballast bed.
U.S. Pat. No. 3,910,195, dated Oct. 7, 1975, discloses a mobile, intermittently advancing track tamper designed to tamp two successive ties during each tamping cycle. The tamping tool assembly of this machine has pairs of opposed reciprocatory and vibratory tamping tools arranged for immersion in the cribs for tamping ballast under the ties and additional vibratory tamping tools arranged for immersion in the ballast adjacent the ends of the ties for reciprocation in the direction of tie elongation whereby a high ballast compaction is obtained at the intersections of the ties and rails where the track rails are supported. Small ballast plows are arranged rearwardly of the tamping tool assemblies at each track shoulder to enable ballast to be moved from the shoulders to the region immediately adjacent the tie ends. This makes it possible for immediately following surface tampers to consolidate or compact the ballast at the tie ends. Such shoulder plows and ballast compactors are not needed in the absence of tie end tamping tools.